1. Field of the Invention
The invention relates generally to ergonomic devices, and more particularly to ergonomic armrest devices.
2. Description of Related Art
Ergonomics is the physical and physiological study of relationships between people and their use of machines and tools. An ergonomic device is designed to reflect human structure and function to enhance and support a person's ability to comfortably perform a task and/or operate a device or apparatus. An ergonomic device or apparatus enhances a person's performance or ability to operate a machine by reducing musculo-skeletal fatigue and injuries caused by repetitive motion or cumulative trauma. Musculo-skeletal disorders in the hand, wrist, arm and shoulder are caused by continuous and repetitious hand, wrist, or arm functions, awkward postures, forceful exertions, or a combination. In a computerized environment, personnel may spend their entire workdays at computer terminals with their forearms extended over computer keyboards or utilizing a pointer. Postal workers may spend extended periods of time with their forearms extended to operate coding machines for coding and sorting mail. Assembly-line personnel may also work with their forearms extended over articles of manufacture to manipulate tiny parts with their fingers. Often, work environments lead to severe and sometimes permanent disabling injuries. At Lawrence Berkeley National Laboratory, 60% of current reported injuries are ergonomically based within computer environments. A dynamic ergonomic arm support device would be highly advantageous in these and other workplaces.
Ergonomic armrest assemblies are known, and examples are illustrated in various prior art patents. In general, many adjustable height armrest assemblies include a support member interconnected with the seat or base of the chair and extending upwardly from the seat adjacent a side of the seat, and an armrest assembly slidably mounted to the support member. The armrest assembly typically includes an armrest and a depending tubular member defining an internal passage within which the support member is slidably received. The tubular member telescopes relative to the support member to adjust the height of the armrest relative to the seat. A movable latch is interconnected with the armrest assembly, and is selectively engageable with one of a series of spaced notches or the like formed in or on the support member. In some versions, the latch has a manually engageable trigger section that selectively moves the latch into or out of engagement with the notches. In other versions, the latch is internal and is engageable with an actuator arrangement for selectively moving the latch between engaged and disengaged positions, depending upon the position of the armrest relative to the support member
One problem with some existing ergonomic arm support systems is that they have limited support and range of motion, and tend to break when leaned on. Typically, a worker may lean and exert downward pressure or weight on the cushioned or distal end of the arm of the conventional arm support which is intended for supporting only the weight of a forearm. The leverage or force exerted by the weight of such a lean or end loading is magnified by the overall length of the two arms of the jointed arm support.
Another problem is that conventional arm supports may not decrease substantially the risk of musculoskeletal disorders, such as carpal tunnel syndrome. This syndrome may be caused at least in part by the tendency of a keyboard operator to rest his or her wrists on the keyboard, or on a portion of the table immediately in front of the keyboard, while his or her hands are elevated relative to the wrists for operation of the keyboard. With the long reach of the two-arm jointed arm support, and the attendant amount of leverage, the arm cushion on the distal end of the second arm may sink to the table surface even under the relatively light weight of an arm. Even providing for height adjustment, such instability or deflection of the second arm may not provide a sufficient lift for the wrists to be held at the proper elevation relative to the hands to minimize the risk of carpal tunnel syndrome or other musculoskeletal disorders.
Computer based typing tasks involve supporting the hands over a keyboard for long periods of time. This creates significant levels of stress in the muscle areas of the wrist, forearm and elbow. The structural dynamics associated with this work environment involve holding the wrists and lower arm in a horizontal position for extended periods of time while typing. The inefficient attachment points of the muscles in the arms create a significant level of difficulty in holding the lower arm in a horizontal position. This creates a significant level of stress in the lower muscles, leading to fatigue and microtrauma.
A major problem with prior art armrests, including supposedly ergonomic systems, is that the devices are static in nature. While the armrests may be adjustable, they are adjusted into various fixed positions. The fixed position may not be optimal for all users or uses, and readjustment may be difficult or inconvenient. What is really desired is a dynamic armrest system that dynamically balances the forces and maintains an ergonomically safe position of a user's arms over a user's range of movements and upper extremity positions.